Effect of dietary fibre on the energy value of feeds for pigs

Dietary fibre (DF) is an inevitable component of organic matter in pig feed s since it is present in most ingredients and to a high extent in by-produc ts (wheat bran or corn gluten feed, for instance) or forages which are more commonly used. In growing pigs, digestibility coefficients of DF average 0 .40-0.50 but they range from around zero in high lignin and water-insoluble DF sources (e.g. wheat straw) to 0.80-0.90 in fibre sources with high pect in or water-soluble DF levels (e.g. sugar beet pulp or soybean hulls). This also means that components of DF are digested differently by pigs: lignin is undigested while pectins are almost totally digested; hemicellulose tend s to be more digested than cellulose, although both are partly digested. Ho wever, even if it is partly digested, DF provides negligible amounts of dig estible or metabolisable energy to the growing pig due to increased endogen ous protein and fat losses and negative interactions between DF and other d ietary components. Digestive utilisation of DF improves with body weight of the pig with the highest values obtained in adult sows. However, this impr ovement is dependent on the botanical origin of DE Consequently, DF makes a positive contribution to energy supply in adult sows and it is therefore r ecommended to give at least two energy values for pig feeds: one for growin g pigs and one for adult sows. Digestion of DF is also associated with ener gy losses as methane. The efficiency of utilisation of metabolisable energy for net energy is poorer when it originates from DF (0.50-0.60 versus 0.80 for starch). Finally, the actual contribution of dietary fibre to energy b alance of the pig can be affected by climatic conditions (heat increment of DF is used for thermoregulation) or changes in behaviour of pigs (lower ph ysical activity with higher DF supply). (C) 2001 Elsevier Science B.V. All rights reserved.